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19-1805; Rev 0; 12/00
800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
General Description
The MAX1765 is a high-efficiency, low-noise, step-up DC-DC converter intended for use in battery-powered wireless applications. This device operates at a high 1MHz fixed frequency while maintaining an exceptionally low quiescent supply current (200A). Its small external components and tiny package make this device an excellent choice for small hand-held applications that require the longest possible battery life. The MAX1765 uses a synchronous-rectified pulsewidth-modulation (PWM) boost topology to generate 2.5V to 5.5V outputs from a wide range of input sources, such as one to three alkaline or NiCd/NiMH cells or a single lithium-ion (Li+) cell. Maxim's proprietary architecture significantly improves efficiency at low load currents while automatically transitioning to fixed-frequency PWM operation at medium to high load currents to maintain excellent full-load efficiency. Forced-PWM mode is available for applications that require constant-frequency operation at all load currents, and the MAX1765 may also be synchronized to an external clock to protect sensitive frequency bands in communications equipment. The MAX1765's low-dropout (LDO) linear regulator and DC-DC converter have separate shutdown control. The linear regulator's 250m pass device maintains excellent dropout voltage at currents up to 500mA. The MAX1765 also features analog soft-start and currentlimit functions to permit optimization of efficiency, external component size, and output voltage ripple. The MAX1765 comes in a 16-pin QSOP package and a thermally enhanced 16-pin TSSOP-EP.
____________________________Features
o High-Efficiency Step-Up Converter Up to 93% Efficiency Adjustable Output from +2.5V to +5.5V Up to 800mA Output PWM Synchronous-Rectified Topology 1MHz Operating Frequency (or Sync) o LDO Linear Regulator 500mA LDO Linear Regulator 2.85V Linear Regulator Output or Adjustable (1.25V to 5V) Low 125mV Dropout at 500mA o +0.7V to +5.5V Input Range o 0.1A Logic-Controlled Shutdown o Adjustable Inductor Current Limit and Soft-Start o Thermal Shutdown o 1.5W, 16-Pin TSSOP-EP Package Available
Ordering Information
PART MAX1765EEE MAX1765EUE TEMP. RANGE -40C to +85C -40C to +85C PIN-PACKAGE 16 QSOP 16 TSSOP-EP*
*Exposed pad
Applications
Wireless Handsets PCS Phones Palmtop Computers Personal Communicators Hand-Held Instruments Portable Audio Players
Typical Operating Circuit
TOP VIEW
(0.7V TO 5.5V) 3.3H ONL LX ONB CLK/SEL TRACK MAX1765 REF ILIM OUTL = 2.85V (ADJ 1.25V TO 5V) ONA POUT INL OUT FB OUT = 3.3V
FBL 1 ISET 2 REF 3 GND 4 FB 5 OUT 6 ONA 7 CLK/SEL 8
Pin Configuration
16 ONL 15 TRACK 14 OUTL
MAX1765
13 INL 12 POUT 11 LX 10 PGND 9 ONB
OUTL GND FBL PGND
QSOP/TSSOP-EP ________________________________________________________________ Maxim Integrated Products 1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
ABSOLUTE MAXIMUM RATINGS
ONA, ONB, ONL, TRACK, OUT, INL to GND..............-0.3V, +6V PGND to GND.....................................................................0.3V LX to GND ...............................................-0.3V to (POUT + 0.3V) OUTL to GND ..............................................-0.3V to (INL + 0.3V) CLK/SEL, REF, FB, FBL, ISET, POUT to GND...................................................-0.3V to (OUT + 0.3V) OUTL Short Circuit .....................................................Continuous Continuous Power Dissipation (TA = +70C) 16-Pin QSOP (derate 8.3mW/C above +70C)...........667mW 16-Pin TSSOP-EP (derate 19mW/C above +70C) ....1500mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VOUT = VPOUT = VINL = VONA = VONL = 3.6V, CLK/SEL = FBL = ONB = TRACK = PGND = GND, ISET = REF (bypassed with 0.22F), LX = open, OUTL = open (bypassed with 4.7F), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER DC-DC CONVERTER Input Voltage Range INL Voltage Range Minimum Startup Voltage Temperature Coefficient of Startup Voltage FB Regulation Voltage FB Input Leakage Current Output Voltage Adjust Range Load Regulation OUT Voltage in Track Mode Frequency in Startup Mode Startup to Normal Mode Transition Voltage ISET Input Leakage Current Supply Current in Normal Mode (Note 3) Supply Current in Low-Noise PWM Mode (Note 3) Supply Current in Shutdown fLX CLK/SEL = OUT, 0 < ILOAD < 800mA VOUTL > 2.0V, INL = POUT VOUT = 1.5V Rising edge only (Note 2) VISET = 1.25V CLK/SEL = ONL = GND, no load CLK/SEL = OUT, no load VFB = 1.5V FB = GND (LX switching) VOUTL + 0.4 125 2.00 2.15 0.01 100 130 2.5 1 10 VFB (Note 1) (Note 1) ILOAD < 1mA, TA = +25C, Figure 2 ILOAD < 1mA CLK/SEL = OUT, 0 < ILX < 0.55A VFB = 1.35V 2.5 -1 VOUTL + 0.5 VOUTL + 0.6 1000 2.30 50 200 200 1.215 0.7 2.3 0.9 -2 1.250 0.01 1.275 100 5.5 5.5 5.5 1.1 V V V mV/C V nA V % V kHz V nA A A mA A SYMBOL CONDITIONS MIN TYP MAX UNITS
ONA = ONL = GND, ONB = OUT
2
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)
(VOUT = VPOUT = VINL = VONA = VONL = 3.6V, CLK/SEL = FBL = ONB = TRACK = PGND = GND, ISET = REF (bypassed with 0.22F), LX = open, OUTL = open (bypassed with 4.7F), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER DC-DC SWITCHES POUT Leakage Current LX Leakage Current Switch On-Resistance N-Channel Current Limit (Note 4) P-Channel Turn-Off Current REFERENCE Reference Output Voltage Reference Load Regulation Reference Supply Regulation LINEAR REGULATOR INL Voltage Range INL Startup Voltage Output Voltage in Internal Feedback Mode FBL Dual-Mode Threshold FBL Regulation Voltage FBL Input Leakage Current OUTL Adjust Range Short-Circuit Current Limit Dropout Resistance Load Regulation Line Regulation INL Supply Current in Shutdown INL No-Load Supply Current AC Power-Supply Rejection Thermal Shutdown VFBL = 1V VFBL = 1V, IOUTL = 500mA 1mA < IOUTL < 500mA, FBL = GND 2.5V < (VOUT = VINL = VPOUT) < 5.5V, FBL = OUTL OUTL = ONA = ONL = GND IOUTL = 0, VINL = 5.5V f = 10kHz Hysteresis approximately 10C -0.5 0.1 90 65 160 VFBL FBL = OUTL, IOUTL = 10mA, IREF = 0 VFBL = 1.5V 1.25 550 0.25 0.5 VINL (Note 1) VOUT = 2V, rising edge only FBL = GND, IOUTL = 10mA 2.15 2.80 150 1.230 2.3 2.30 2.85 250 1.250 0.01 5.5 2.45 2.90 350 1.270 50 5 1300 0.5 1 0.5 10 250 V V V mV V nA V mA % % A A dB C VREF IREF = 0 -1A < IREF < 50A 2.5V < VOUT < 5.5V 1.230 1.250 5 0.2 1.270 15 5 V mV mV ILIM VLX = 0, VOUT = 5.5V VLX = VOUT = V ONB = 5.5V, ONA = GND N-channel P-channel VISET = 1.25V, CLK/SEL = GND or OUT CLK/SEL = GND 1000 10 0.1 0.1 0.17 0.22 1250 50 10 10 0.28 0.5 1600 120 A A mA mA SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX1765
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
ELECTRICAL CHARACTERISTICS (continued)
(VOUT = VPOUT = VINL = VONA = VONL = 3.6V, CLK/SEL = FBL = ONB = TRACK = PGND = GND, ISET = REF (bypassed with 0.22F), LX = open, OUTL = open (bypassed with 4.7F), TA = 0C to +85C, unless otherwise noted. Typical values are at TA =+25 C.)
PARAMETER CONTROL INPUTS ONA, ONB, ONL (Note 5) Input Low Level CLK/SEL TRACK ONA, ONB, ONL (Note 5) Input High Level CLK/SEL TRACK Input Leakage Current (CLK/SEL, ONA, ONB, ONL, TRACK) Internal Oscillator Frequency External Oscillator Synchronization Range Oscillator Maximum Duty Cycle Minimum CLK/SEL Pulse Maximum CLK/SEL Rise/Fall Time CLK/SEL = OUT 0.8 0.5 80 86 200 100 1.1V < VOUT < 1.8V 1.8V < VOUT < 5.5V 1.2V < VOUT < 5.5V 1.2V < VINL < 5.5V 1.1V < VOUT < 1.8V 1.8V < VOUT < 5.5V 1.2V < VOUT < 5.5V 1.2V < VINL < 5.5V VOUT - 0.2 1.6 0.8 x VOUT 0.8 x VINL 0.01 1 1 1.2 1.2 90 A MHz MHz % ns ns V 0.2 0.4 0.2 x VOUT 0.2 x VINL V SYMBOL CONDITIONS MIN TYP MAX UNITS
4
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator
ELECTRICAL CHARACTERISTICS
(VOUT = VPOUT = VINL = VONA = VONL = 3.6V, CLK/SEL = FBL = ONB = TRACK = PGND = GND, ISET = REF (bypassed with 0.22F), LX = open, OUTL = open (bypassed with 4.7F), TA = -40C to +85C, unless otherwise noted.) (Note 6)
PARAMETER DC-DC CONVERTER FB Regulation Voltage OUT Voltage in Track Mode Startup to Normal Mode Transition Voltage Supply Current in Normal Mode (Note 3) Supply Current in Low-Noise PWM Mode (Note 3 Supply Current in Shutdown DC-DC SWITCHES POUT Leakage Current LX Leakage Current Switch On-Resistance N-Channel Current Limit (Note 4) P-Channel Turn-Off Current REFERENCE Reference Output Voltage LINEAR REGULATOR Output Voltage in Internal Feedback Mode FBL Input Threshold FBL Regulation Voltage LDO Startup Voltage Dropout Resistance INL Supply Current in Shutdown INL No-Load Supply Current FBL = OUTL, IOUTL = 10mA, IREF = 0 VOUT = 2V, rising edge only VFBL = 1V, IOUTL = 500mA OUTL = ONA = ONL = GND IOUTL = 0, VINL = 5.5V FBL = GND, IOUTL = 10mA 2.79 150 1.225 2.15 2.90 350 1.275 2.45 0.5 10 250 V mV V V A A IREF = 0 1.225 1.275 V ILIM VLX = 0, VOUT = 5.5V VLX = VOUT = V ONB = 5.5V, ONA = GND N-channel P-channel VISET = 1.25V, CLK/SEL = GND or OUT CLK/SEL = GND 1000 5 10 10 0.28 0.50 1600 120 A A mA mA VFB CLK/SEL = OUT, 0 < ILX < 0.55A VOUTL > 2.0V, INL = POUT Rising edge only (Note 2) CLK/SEL = ONL = GND, no load CLK/SEL = OUT, VFB = 1.5V, no load ONA = ONL = GND, ONB = OUT 1.210 VOUTL + 0.4 2.00 1.280 VOUTL + 0.6 2.30 200 200 10 V V V A A A SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX1765
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5
800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
ELECTRICAL CHARACTERISTICS (continued)
(VOUT = VPOUT = VINL = VONA = VONL = 3.6V, CLK/SEL = FBL = ONB = TRACK = PGND = GND, ISET = REF (bypassed with 0.22F), LX = open, OUTL = open (bypassed with 4.7F), TA = -40C to +85C, unless otherwise noted.) (Note 6)
PARAMETER CONTROL INPUTS ONA, ONB, ONL (Note 5) Input Low Level CLK/SEL TRACK ONA, ONB, ONL (Note 5) Input High Level CLK/SEL TRACK Input Leakage Current (CLK/SEL, ONA, ONB, ONL, TRACK) Internal Oscillator Frequency Oscillator Maximum Duty Cycle CLK/SEL = OUT 0.8 79 1.1V < VOUT < 1.8V 1.8V < VOUT < 5.5V 1.2V < VOUT < 5.5V 1.2V < VINL < 5.5V 1.1V < VOUT < 1.8V 1.8V < VOUT < 5.5V 1.2V < VOUT < 5.5V 1.2V < VINL < 5.5V VOUT - 0.2 1.6 0.8 x VOUT 0.8 x VINL 1 1.2 90 A MHz % V 0.2 0.4 0.2 x VOUT 0.2 x VINL V SYMBOL CONDITIONS MIN TYP MAX UNITS
Note 1: Operating voltage. Since the regulator is bootstrapped to the output, once started it will operate down to 0.7V input. Note 2: The device is in startup mode when VOUT is below this value (see Low-Voltage Startup Oscillator section). Do not apply full load current. Note 3: Supply current into the OUT and POUT pins. This current correlates directly to the actual battery-supply current, but is reduced in value according to the step-up ratio and efficiency. Note 4: Minimum recommended ISET voltage in normal mode is 0.625V. Note 5: ONA, ONB, ONL have hysteresis of approximately 0.15 VOUT. Note 6: Specifications to -40C are guaranteed by design and not production tested.
6
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
MAX1765
EFFICIENCY vs. LOAD CURRENT (VOUT = +3.3V)
MAX1765 toc01
EFFICIENCY vs. LOAD CURRENT (VOUT = +5V)
MAX1765 toc02
TRACK MODE EFFICIENCY vs. LOAD CURRENT (VOUTL = +2.85V)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VIN = +1.2V VIN = +2.4V VIN = +1.2V PWM MODE VIN = +2.4V NORMAL MODE
MAX1765 toc03
1.0 0.9 0.8 EFFICIENCY (%) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
VIN = +2.4V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0
VIN = +3.6V NORMAL MODE VIN = +2.4V VIN = +1.2V PWM MODE VIN = +1.2V VIN = +2.4V VIN = +3.6V
100
NORMAL MODE
VIN = +1.2V PWM MODE VIN = +2.4V
VIN = +1.2V
0.001
0.01
0.1
1
0.001
0.01
0.1
1
0.001
0.01
0.1
1
LOAD CURRENT (A)
LOAD CURRENT (A)
LOAD CURRENT (A)
TRACK MODE EFFICIENCY vs. LOAD CURRENT (VOUTL = +3.3V)
MAX1765 toc04
TRACK MODE EFFICIENCY vs. LOAD CURRENT (VOUTL = +5V)
NORMAL MODE VIN = +3.6V
MAX1765 toc05
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
VOUT = +5V, ISET = REF 1000 OUTPUT CURRENT (mA) 800 600 400 200 VOUT = +5V, ISET = 0.5 REF 0 VOUT = +3.3V, ISET = 0.5 REF VOUT = +3.3V, ISET = REF
MAX1765 toc06
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0.001 0.01 NORMAL MODE
VIN = +2.4V
VIN = +3.6V
90 80 70 EFFICIENCY (%) 60 50
1200
VIN = +2.4V
VIN = +1.2V
PWM MODE NORMAL MODE/ PWM MODE
VIN = +2.4V
VIN = +1.2V
PWM MODE
VIN = +1.2V
40 30 20 10 0 VIN = +1.2V VIN = +2.4V VIN = +3.6V 0.001 0.01 0.1 1
0.1
1
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V)
LOAD CURRENT (A)
LOAD CURRENT (A)
LINEAR REGULATOR DROPOUT VOLTAGE vs. LOAD CURRENT
MAX1765 toc07
STARTUP INPUT VOLTAGE vs. OUTPUT CURRENT
MAX1765 toc08
NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE
16 SUPPLY CURRENT (mA) 14 12 10 8 6 4 2 NORMAL MODE 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 FPWM MODE
MAX1765 toc09
0.30 0.25 DROPOUT VOLTAGE (V) VOUTL = +2.5V 0.20 VOUTL = +2.85V 0.15 0.10 VOUTL = +5V 0.05 0 0
2.5 TA = +25C TA = -40C
18
STARTUP INPUT VOLTAGE (V)
2.0
1.5
1.0 TA = +85C 0.5
0 100 200 300 400 500 600 700 800 LOAD CURRENT (mA) 1 10 100 1000 OUTPUT CURRENT (mA)
0 INPUT VOLTAGE (V)
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
LDO PSRR vs. FREQUENCY (100Hz TO 1MHz)
0 -10 -20 NOISE (mVRMS) LDO PSRR (dB) -30 -40 -50 -60 -70 -80 0.1 1 10 FREQUENCY (kHz) 100 1000 0.1 1 FREQUENCY (MHz) 10 16 14 12 10 8 6 4 2 0 VIN = +2.4V VOUT = +3.3V
BOOST FOLLOWED BY LDO OUTPUT NOISE SPECTRUM
MAX1765 toc10 MAX1765 toc11
LINE TRANSIENT RESPONSE (DC-DC)
MAX1765 toc12
A
B
100s/div A: VIN, 500mV/div VOUT = +3.3V, I = 0mA B: VOUT, 1mV/div, AC-COUPLED VIN = +1.4V TO +2.4V
LINE TRANSIENT RESPONSE (LINEAR)
MAX1765 toc13
LOAD TRANSIENT RESPONSE
MAX1765 toc14
TURN-ON WAVEFORMS NO SOFT-START COMPONENTS
MAX1765 toc15a
A A
A
B
B
B
C
I = 0mA, VIN = +3V TO +5V, VOUT = +3.3V A: VIN, 2V/div B: VOUT, 5mV/div, AC-COUPLED
50s/div VIN = +2.4V, VOUT = +3.3V, IOUT = 0 TO 500mA A: IOUT, 500mA/div B: VOUT,100mV/div
A: 0NA, 5V/div B: VOUT, 2V/div C: INPUT CURRENT, 1A/div
SOFT-START WAVEFORMS (RSS = 500k, CSS = 0.1F)
MAX1765 toc15b
HEAVY-LOAD SWITCHING WAVEFORMS (IOUT = 650mA, VIN = +2.4V, VOUT = 3.3V)
MAX1765 toc16
A
A
B
B
C C 2.5ms/div A: 0NA, 5V/div B: INPUT CURRENT, 100mA/div C: VOUT, 1V/div 500ns/div A: LX, 5V/div B: INDUCTOR CURRENT, 200mA/div C: OUTPUT RIPPLE, 50mV/div, AC-COUPLED
8
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
LIGHT-LOAD SWITCHING WAVEFORMS (VIN = +2.4V, VOUT = +3.3V, IOUT = 10mA)
MAX1765 toc17
LINEAR-REGULATOR OUTPUT NOISE
MAX1765 toc18
SWITCH CURRENT LIMIT vs. VISET
VOUT = +3.3
MAX1765 toc19
450 ILDO = 200mA VLDO = 2.85V
1.4 1.2 SWITCH CURRENT LIMIT (A) 1.0 0.8 0.6 0.4 0.2 0 0
A NOISE (mVRMS)
350
250
B
150
C 50 0 500ns/div 0.1 1 FREQUENCY (MHz) 10
A: LX NODE, 5V/div B: INDUCTOR CURRENT, 200mA/div, AC-COUPLED C: OUTPUT RIPPLE, 20mV/div, AC-COUPLED
0.2
0.4
0.6
0.8
1.0
1.2
1.4
VISET (V)
Pin Description
PIN NAME FUNCTION Low-Dropout Linear Regulator Dual-Mode Feedback Input. Connect FBL to ground for 2.85V nominal output voltage. Connect FBL to a resistor-divider from OUTL to ground for an adjustable output voltage. FBL regulates to 1.25V. Set N-Channel Current Limit. For maximum current limit, connect ISET to REF. To reduce current limit, use a resistor-divider from REF to GND. If soft-start is desired, a capacitor can be added from ISET to GND. When ONA = LO and ONB = HI or VREF < 80% of nominal value, an on-chip 100k switchable resistor discharges ISET to GND. 1.25V Reference Output. Connect a 0.22F bypass capacitor to GND; 50A of external load current is allowed. The reference is enabled if ONA = HI, ONB = LO, or ONL = HI. Ground. Connect to PGND with short trace. Boost Converter Feedback Input. Connect a resistor-divider between OUT and GND to set the output voltage in the range of 2.5V to 5V. In track mode, FB is disabled after OUTL is in regulation. Boost Converter IC power is derived from OUT. Connect OUT to POUT through a 4.7 resistor and bypass to GND with a 0.68F capacitor. ON Input. When high, the DC-DC is operational (Table 2). CLOCK Input for the DC-DC Converter. Also serves to program operating mode of switch as follows: CLK/SEL = LOW: Normal mode. Operates at a fixed frequency, automatically switching to lowpower (SKIP) mode when the load is minimized. CLK/SEL = HI: Forced PWM mode. Operates in low-noise, constant-frequency mode at all loads. CLK/SEL = Clocked: Synchronized forced PWM mode. The internal oscillator is synchronized to an external clock in the 500kHz to 1200kHz frequency range.
1
FBL
2
ISET
3 4 5 6 7
REF GND FB OUT ONA
8
CLK/SEL
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
Pin Description (continued)
PIN 9 10 11 12 13 14 NAME ONB PGND LX POUT INL OUTL FUNCTION ON Input. When low, the DC-DC is operational (Table 2). Power Ground Inductor connection to the drain of P-channel synchronous rectifier and N-channel switch. Boost Converter Power Output. POUT is the source of the P-channel synchronous-rectifier MOSFET switch. Connect POUT to INL. Bypass POUT to PGND with a 100F capacitor. Linear Regulator Power Input. Source of PFET pass device connected between INL and OUTL. Connect INL to POUT. Linear Regulator Output. OUTL can source up to 500mA. Bypass OUTL to GND with a 4.7F capacitor. Track-Mode Control Input for DC-DC Converter. In track mode, the boost converter output is sensed at OUT and set to 0.5V above OUTL to improve efficiency. Set TRACK to OUT for track mode and to GND for normal operation (Table 2). Linear Regulator ON Input. Enables the linear regulator output when TRACK = LOW. ONA and ONB determine the linear regulator's output state when TRACK = HIGH.
15
TRACK
16
ONL
Detailed Description
The MAX1765 is a highly efficient, low-noise power supply for portable RF hand-held instruments. This boost power supply combines an LDO linear regulator, a low-noise, high-power, step-up switching regulator, an N-channel power MOSFET, a P-channel synchronous rectifier, shutdown control, and a precision voltage reference in a single 16-pin QSOP or a thermally enhanced TSSOP-EP (Figure 1). The switching DC-DC converter boosts a 1-cell to 3-cell NiMH/NiCd or a single Li+ battery input to an adjustable output voltage between 2.5V and 5.5V. The MAX1765 guarantees startup with voltages as low as 1.1V and will remain operational down to 0.7V (Figure 2). The internal LDO regulator provides linear postregulation for noise-sensitive circuitry, or it can be used as a separate voltage output adjustable from 1.25V up to POUT. The MAX1765 is optimized for use in cellular phones and other applications requiring low noise during fullpower operation, as well as low quiescent current for maximum battery life during standby and shutdown. The device automatically transitions to a low-quiescentcurrent pulse-skipping control scheme during light loads that reduces the quiescent power consumption to 360W. The supply current of the device can be further reduced to 1A when the device is shut down. Figure 2 shows a typical application of the MAX1765 in normal mode.
10
The switching regulator supports two low-noise modes: fixed-frequency PWM for low noise in all load conditions, and synchronization of the internal oscillator to an external clock driving the CLK input. In TRACK mode, the DC and linear regulator work together to maintain excellent PSRR without excessive efficiency loss. Additional MAX1765 features include synchronous rectification for high efficiency and increased battery life, dual boost shutdown controls for P or a pushbutton momentary switch, and a separate shutdown control for the linear regulator.
Step-Up Converter
During DC-DC converter operation, the internal N-channel MOSFET turns on for the first part of each cycle, allowing current to ramp up in the inductor and store energy in a magnetic field. During the second part of each cycle, the MOSFET turns off and inductor current flows through the synchronous rectifier to the output filter capacitor and the load. As the energy stored in the inductor is depleted, the current ramps down and the synchronous rectifier turns off. The CLK/SEL pin determines whether a pulse-skipping or PWM control method is used at light loads (Table 1).
Normal Operation
Pulling CLK/SEL low selects the MAX1765's normal operating mode. In this mode, the device operates in PWM when driving medium to heavy loads and automatically switches to SKIP mode if the load requires
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
MAX1765
THERMAL SENSOR
SHUTDOWN LOGIC FBL OUT ONL IC PWR 2.15V GND ONA ONB ONL REF CLK/SEL VOUT FB VOUT - 300mV TRACK ISET IFB ISET ON RDY REF ERROR AMP MOSFET DRIVER WITH CURRENT LIMITING
INL
P
OUTL
POUT TRACK EN STARTUP OSCILLATOR Q D Q PWM CONTROLLER EN OSC EN 1MHz OSCILLATOR SKIP/PWM MODE IREF PGND N LX P
1.250V REFERENCE
Q
ICS
Figure 1. Functional Diagram
Table 1. Selecting the Operating Mode
CLK/SEL MODE FEATURES High-efficiency pulse skipping at light loads, PWM at medium and heavy loads Low noise, fixed frequency at all loads Low noise, fixed frequency at all loads
less power. SKIP mode allows higher efficiency than PWM under light-load conditions. Light-Load Operation in Normal Mode At light loads, the MAX1765 operates by turning on the DC-DC converter's N-channel field-effect transistor (FET) when VFB < VREF, synchronized with the rising edge of the oscillator. The N-channel FET will remain on, ramping up the inductor current past the minimum inductor current, until the internal error amplifier and current mode circuitry determine that the needs of the system have been met or the device hits the ISET current limit. The N-channel is then turned off and the Pchannel is turned on until current decays to the P-channel turn-off current level. The N-channel will remain off until VFB is again less than VREF, and a rising edge of the oscillator occurs.
0
Normal Operation
1 External Clock 500kHz to 1.2MHz
Forced PWM
Synchronized PWM
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11
800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
VIN 0.7V to 3.2V 33F 3.3H VOUT 3.3V 100F
zero detect circuitry is deactivated in forced PWM mode. This means an N- or P-channel FET is on all the time for most load conditions. At light loads, the P-channel will remain on so the device can pass current back to the input from the output. The P-channel will only pass current for two cycles before it is disabled. Then, the device remains inactive until VFB < VREF. During forced PWM operation, the MAX1765 switches at a constant frequency (1MHz) and modulates the MOSFET switch pulse width to control the power transferred per cycle in order to regulate the output voltage for most output currents. Switching harmonics generated by fixed-frequency operation are consistent and easily filtered. (See the Boost Followed by LDO Output Noise Spectrum plot in the Typical Operating Characteristics.)
REF ILIM 0.22F ONA LOGIC INPUTS
LX POUT INL OUT 4.7
MAX1765
FB
0.68F
165k
ONB TRACK ONL
100k VOUTL = 2.85V OUTL 4.7F
FBL GND CLK/SEL PGND
Synchronized PWM Operation
The MAX1765 can be synchronized in PWM mode to an external frequency of 500kHz to 1.2MHz by applying an external clock signal to CLK/SEL. This allows interference to be minimized in wireless applications. The synchronous rectifier is active during synchronized PWM operation.
Figure 2. Typical Application Circuit
Synchronous Rectifier
PWM Operation in Normal Mode The MAX1765 transitions to fixed-frequency PWM operation under medium and heavy loads. The N-channel FET is engaged when VFB < VREF and is kept on to ramp up the current in the inductor until one of the following conditions occurs: the system needs are met, the next falling edge of the internal oscillator is achieved, or the maximum inductor current (ISET) is reached. The N-channel is turned off, activating the Pchannel synchronous rectifier that remains on until the inductor current gets to the P-channel turn-off current level, or VFB < VREF and there is a rising oscillator clock edge. The 1MHz fixed-frequency operation produces an easily filtered fixed-noise spectrum. The MAX1765 features an internal 250m, P-channel synchronous rectifier to enhance efficiency. Synchronous rectification provides a 5% efficiency improvement over similar nonsynchronous boost regulators. In PWM mode, the synchronous rectifier is turned on during the second portion of each switching cycle. At light loads (in normal mode), an internal comparator turns on the synchronous rectifier when the voltage at LX exceeds the boost regulator output, and turns it off when the inductor current drops below 50mA.
Low-Voltage Startup Oscillator
The MAX1765 uses a low-voltage startup oscillator for a 1.1V guaranteed minimum input startup input voltage. A Schottky diode placed across LX and POUT reduces the startup voltage to 0.9V. At startup, the low-voltage oscillator switches the N-channel MOSFET until the output voltage reaches 2.15V. Above this level, the normal boost-converter feedback and control circuitry takes over. Once the device is in regulation, it can operate down to 0.7V input since internal power for the IC is bootstrapped from the OUT pin. Do not apply full load until the output exceeds 2.3V.
Forced PWM Operation
When CLK/SEL is high, the MAX1765 operates in a lownoise PWM-only mode. The N-channel FET is turned on when VFB < VREF and is kept on to ramp up the inductor current until one of the following conditions occurs: the system needs are met, the next falling edge of the internal oscillator is achieved, or the ISET is reached. The N-channel is then turned off, activating the P-channel synchronous rectifier that remains on until the next rising edge of the oscillator, where the N-channel is again turned on under most conditions. The P-channel
12
Linear Regulator
The MAX1765 contains an LDO with a fixed 2.85V (or adjustable) output. The MAX1765 linear regulator fea-
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator
tures a 250m, P-channel MOSFET pass transistor. This provides several advantages, including longer battery life, over similar designs using a PNP pass transistor. The P-channel MOSFET requires no base-drive current. This reduces quiescent current considerably, since PNP-based regulators tend to waste base-drive current in dropout when the pass transistor saturates. Connect the input of the linear regulator (INL) to POUT. The linear regulator can be used to postfilter the switching regulator or regulate a separate supply voltage. This regulated output is intended to power noise-sensitive analog circuitry, such as low-noise amplifiers and IF stages in cellular phones and other instruments, and can deliver up to 500mA. Use a 4.7F capacitor with less than a 1 equivalent series resistance (ESR) on the output to provide stability. The linear regulator has an internal 1.3A (max) current limit and thermal-overload protection circuitry to protect this output.
MAX1765
INPUT 0.7V TO 5.5V
LX
*
OUT SHDN ONB ONA CLK/SEL ONL POUT TRACK INL 33F REF OUTL ILIM 0.22F GND FB FBL PGND 4.7F VOUT = 2.5V - 5.0V AT 500mA
MAX1765
*
Configurations
There are several useful circuit configurations that can be implemented with the MAX1765. The TRACK input divides the circuit configurations into two types, one where the DC-DC converter tracks to the LDO output, and the other where the boost and the LDO regulate independently. Track Mode Asserting the TRACK input places the MAX1765 into track mode, where the DC-DC switching regulator's feedback pin (FB) is ignored, and the boost output (POUT) "tracks" to 500mV above the linear regulator output. The primary use of the MAX1765 in TRACK mode is as a simple or very-low-noise step-up/down power supply (see Figures 3 and 4; also see the Maximum Output Current vs. Input Voltage plot in the Typical Operating Characteristics.) This circuit operates as a linear regulator when the input supply (a battery) is greater than VLDO. When the battery discharges below VLDO, the DC-DC converter turns on, boosting POUT to a constant 500mV above the linear regulator output. This configuration also allows for true shutdown (see True Shutdown). Dual-Supply Mode When the TRACK input is low, the MAX1765 operates two independent power supplies, a DC-DC converter, and a linear regulator. One such application of this configuration is shown in Figure 4. In this mode, the device generates two boosted voltages from a single battery supply. The DC-DC converter could be used to supply the power amplifier (PA) of a cell phone, while the linear regulator powers the baseband functions within the
*
* OPTIONAL COMPONENTS
Figure 3. Simple Step-Up/Step-Down Converter
phone. Asserting TRACK switches the device into track mode when the high-voltage supply for the PA is no longer needed, thus improving efficiency in standbyreceive mode. When the PA again needs 5V, deassert the TRACK input.
Shutdown
The MAX1765 has a shutdown mode that reduces quiescent current to 1A. During shutdown, the reference, LDO, DC-DC converter, and all feedback and control circuitry are off. Table 2 shows the MAX1765 shutdown truth table. If ONA, ONB, and ONL are all deasserted, the device is shut down. True Shutdown When a typical boost converter is placed into shutdown, current can flow through the body diode of the synchronous rectifier to the load. The MAX1765 can be configured to allow true shutdown as shown in Figure 5. The shutdown function is active low and is connected to both ONA and ONL. When asserted, both the DC-DC converter and the LDO are shut down simultaneously. The LDO acts like a switch in this situation and disconnects the input from the load. Connect FBL to a resistor-divider from VREF to GND (R3 and R4 in Figure 5) so
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13
800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
Table 2. Operating Mode Truth Table
OPERATING MODE Shutdown Track H L Independent Regulation L L DC-DC Only L LDO Only X X L L H L H ON OFF ON X H L X H L OFF ON ON X H L X X H ON ON ON TRACK X H ONA L H ONB H X ONL L X ON ON ON LINEAR REGULATOR OFF DC-DC CONVERTER OFF REF OFF
that VFBL = 0.5V (above the Dual ModeTM threshold) when OUTL is regulated, to ensure that the linear regulator is saturated. Another method to configure the MAX1765 for true shutdown is shown in Figure 6. This shutdown function is active high and connects to the gate of a low-impedance PFET and ONB. The PFET acts like a switch in this situation and disconnects the input from the load. Reference The MAX1765 has an internal 1.25V, 1% reference. Connect a 0.22F ceramic bypass capacitor to GND within 0.2in (5mm) of the REF pin. REF can source up to 50A of external load current. Typically connect ISET to REF to give the MAX1765 full inductor current limit.
Setting the Linear Regulator Voltage The LDO regulation voltage can also be set similarly to the DC-DC converter. Connecting FBL to GND sets the LDO output to 2.85V. To set other output voltages between 1.25V and POUT, connect a resistor-divider from OUTL to FBL to GND (Figure 7). Connect the resistor voltage-divider as close to the IC as possible, within 0.2in (5mm) of FBL. The maximum input bias current for the FBL input is 50nA. Choose R4 of 40k or less, then calculate R3 using: V R3 = R4 OUTL - 1 VFBL where VFBL, the linear regulator feedback set point, is +1.25V.
Design Procedure
Setting DC-DC Converter Voltage
Set the output voltage between +2.5V and +5.5V by connecting a resistor voltage-divider from OUT to FB to GND (Figure 7). Connect the resistor voltage-divider as close to the IC as possible, within 0.2in (5mm) of FB. Choose R2 of 40k or less, then calculate R1 using: V R1 = R2 OUT - 1 VFB where VFB, the boost-regulator feedback set point, is +1.25V. For output voltages above 4V, connect a Schottky diode between LX and POUT to prevent voltage transition from exceeding the LX voltage rating.
Dual Mode is a trademark of Maxim Integrated Products 14
Setting the Switch Current Limit and Soft-Start
The ISET pin adjusts the inductor current limit and implements soft-start. With ISET connected to REF, the inductor current limits at 1.25A. With ISET connected to a resistive divider set from REF to GND, the current limit is reduced according to: RSS2 ILIM = 1.25A RSS1 + RSS2 Implement soft-start by placing a resistor from ISET to REF and a capacitor from ISET to GND (Figure 8). In shutdown, ISET is discharged to GND through an onchip 100k resistor. At power-up, ISET is 0V and the current limit is zero. As the capacitor voltage rises, the
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
INPUT 0.7V TO 5.5V 3.3H TRACK = LOW, VOUT = 5.0V TRACK = HIGH, VOUT = 3.35V LX 33F x 2 4.7 OUT
INPUT
OFF
MAX1765
LX ONB POUT OUT
ON
SHDN OUTPUT
MAX1765
TRACK ON OFF TRACK OFF ON ONL ONB 50k ONA POUT REF INL VLDO = 2.85V 4.7F FB 0.68F 150k
FB
Figure 6. PFET Allows True Boost Shutdown
ILIM 0.22F GND CLK/SEL FBL
OUTL PGND
current limit increases and the output voltage rises. The soft-start time constant is: tRISE = RSSCSS
Figure 4. Dual-Output Power Supply
Placing a capacitor across the lower resistor of the current-limiting resistive divider provides both features simultaneously (Figure 9).
INPUT
Package Selection
LX
ON OFF SHDN ONL ONA
MAX1765
POUT INL
OUTL FBL
OUTPUT
R4
R3
The MAX1765 is available in two packages, a 16-pin QSOP and a thermally enhanced TSSOP-EP. The QSOP is the less expensive of the two packages, and requires a less complex layout design. This layout allows the designer to route underneath the device. The power dissipation for the QSOP is 0.7W. The TSSOP-EP comes with an exposed metal pad that is connected to the substrate of the IC. This increases the power dissipation up to 1.5W for the TSSOP-EP. To achieve maximum power capability, the exposed pad of the TSSOP-EP should be reflowed to a pad with low thermal resistance. For convenience, this pad can be connected to AGND or PGND.
Inductor Selection
Figure 5. LDO Enable Allows True Boost Shutdown
The MAX1765's high switching frequency allows the use of a small surface-mount inductor. For most applications, a 3.3H inductor works well. The inductor should have a saturation current rating exceeding the N-channel switch current limit; however, it is acceptable to bias the inductor current into saturation by as much as 20% if a slight reduction in efficiency is acceptable. Lower current-rated inductors may be
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
used if ISET is employed to reduce the peak inductor current (see Setting the Switch Current Limit and SoftStart). For high efficiency, choose an inductor with a high-frequency core material to reduce core losses. To minimize radiated noise, use a toroid or shielded inductor. See Table 3 for suggested components and Table 4 for a list of component suppliers.
LINEARREGULATOR OUTPUT
OUTL
INL
POUT
STEP-UP OUTPUT
MAX1765
R3 OUT FBL R4 GND FB PGND R2 R1
Output Diode
To assist startup with input voltages below 1.1V or when VOUT is set for >4V, use a Schottky diode--such as a 1N5817, MBR0520L or equivalent--between LX and POUT (Figure 2). The Schottky diode carries current after the synchronous rectifier turns off. Thus, its current rating only needs to be 500mA. Connect the diode as close to the IC as possible. Do not use ordinary rectifier diodes; their slow switching speeds and long reverse-recovery times render them unacceptable. For input voltages over 1.8V, the Schottky diode may improve light-load efficiency.
Figure 7. Feedback Connections
Input and Output Filter Capacitors
Choose input and output filter capacitors that will service the input and output peak currents with acceptable voltage ripple. Choose input capacitors with working voltage ratings over the maximum input voltage and output capacitors with working voltage ratings higher than the output. A 100F, 100m, low equivalent-series-resistance (ESR) tantalum output capacitor is recommended for most applications. At the output of the linear regulator (OUTL), use a 4.7F ceramic capacitor for stability at loads up to 500mA. The input filter capacitor reduces peak currents drawn from the input source and also reduces input switching noise. The input voltage source impedance determines the required size of the input capacitor. When operating directly from one or two NiMH cells placed close to the MAX1765, use a single 33F low-ESR input filter capacitor. The Sanyo POSCAP, Panasonic SP/CB, and Kemet T510 are good low-ESR capacitors. Low-ESR tantalum capacitors offer a good trade-off between price and performance. Do not exceed the ripple current ratings of tantalum capacitors. Avoid aluminum electrolytic capacitors; their high ESR typically results in higher output ripple voltage.
Layout Considerations
High switching frequencies and large peak currents make PC board layout a critical part of design. Poor design will cause excessive EMI and ground bounce, both of which can cause instability or regulation errors by corrupting the voltage and current feedback signals. Power components--such as the inductor, converter IC, filter capacitors, and output diode--should be placed as close together as possible, and their traces should be kept short, direct, and wide. Connect the inductor from the battery to the LX pins as close to the IC as possible. Keep the voltage feedback network very close to the IC, within 0.2in (5mm) of the FB pins. Keep noisy traces, such as those from the LX pin, away from the voltage feedback networks and guarded from them using grounded copper. Refer to the MAX1765 EV kit for a full PC board example.
Applications Information
Use in a Typical Wireless Phone Application
The MAX1765 is ideal for use in digital cordless and PCS phones. The PA is connected directly to the stepup converter output for maximum voltage swing and power efficiency (Figure 10). The internal linear regulator is used for postregulation to generate low-noise power for DSP, control, and RF circuitry. The following equations may be used to estimate the typical available output current under conditions other than those listed here:
Bypass Capacitors
Bypass REF to GND with 0.22F. Also, bypass OUT to GND with a 0.68F ceramic capacitor, and connect OUT to POUT with a 4.7 resistor. Each of these components should be placed as close to its respective IC pins as possible, within 0.2in (5mm).
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
REF 0.22F RSS1
RSS2 ILIM = 1.25A RSS1 + RSS2 tSS = (RSS1 || RSS2) CSS
(
)
0.22F RSS
REF
ILIM = 1.25A tSS = RSS CSS 500k < RSS < 1M
MAX1765
ISET CSS RSS2 CSS ISET
MAX1765
Figure 8. Soft-Start, Reduced Current Limit
Figure 9. Soft-Start, Maximum Current Limit
Table 3. Component Selection Guide
PRODUCTION 3.3H INDUCTORS Coilcraft DS3316P Coilcraft LPT3305 CAPACITORS AVX TPS series Kemet T510 series Sanyo POSCAP series SCHOTTKY DIODES Motorola MBR0520L Nihon EP10QY03
Surface Mount
Table 4. Component Suppliers
SUPPLIER AVX Coilcraft Kemet Motorola Sumida COUNTRY USA USA USA USA Japan USA Japan PHONE 843-448-9411 847-639-6400 810-287-2536 408-629-4789 81-45-474-7030 847-956-0666 81-3-3607-3302
I IOUT,MAX = ILIM - RIPPLE (I - D) 2 IRIPPLE = D= D 1 x x VIN - ILIM x (RNCH + LESR ) fSW L
[
]
VOUT - VIN + ILIM x (RNCH + LESR ) VOUT + ILIM (RPCH - RNCH )
Note: Please indicate that you are using the MAX1765 when contacting these component suppliers.
where ILIM is the peak inductor current limit, fSW is the operating frequency (typically 1.2MHz), L is the inductance of the chosen inductor, LRESR is the resistance of the chosen inductor, RNCH and RPCH are the resistances of the internal N-channel and P-channel, respectively. Table 5 lists the typical available output current when operating with one or more NiCd/NiMH cells or one Li+ cell.
Adding a Manual Power Reset
A momentary pushbutton switch can be used to turn the MAX1765 on and off (Figure 11). ONA is pulled low and ONB is pulled high to turn the device off. When the momentary switch is pressed, ONB is pulled low and
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17
800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator MAX1765
270k
LX CONTROL INPUTS GND POUT INL
C
MAX1765
ONB POUT VDD I/O ONA I/O
MAX1765
OUTL
ON/OFF
I/O C
PA RF
0.1F
270k
Figure 10. Typical Phone Application Figure 11. Momentary Pushbutton On/Off Switch
Table 5. Typical Available Output Current
NUMBER OF CELLS 1 NiCd/NiMH 2 NiCd/NiMH 2.4 3 NiCd/NiMH or 1 Li+ 3.6 5.0 5.0 460 720 INPUT VOLTAGE (V) 1.2 2.4 OUTPUT VOLTAGE (V) 3.3 3.3 OUTPUT CURRENT (mA) 330 730
the regulator turns on. The switch must be pressed long enough for the microcontroller (C) to exit reset and drive ONA high. A small capacitor is added to help debounce the switch. The C issues a logic high to ONA, which holds the device on, regardless of the switch state. To turn the regulator off, press the switch again, allowing the C to read the switch status and pull ONA low. When the switch is released, ONB is pulled high.
Chip Information
TRANSISTOR COUNT: 1735
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800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator
Package Information
QSOP.EPS
MAX1765
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________19 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
TSSOP, 4.0,EXP PADS.EPS

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